The present invention generally relates to a method for determining the probability that an event has occurred at a set of spatially localized positions in the environment, and more particularly to modeling of multisensory processing in brain maps.
All vertebrate animals constantly monitor the environment by orienting their sensory organs toward the locations of events of potential survival value. Neurobiological evidence indicates that animals utilize multisensory integration to detect the targets of orienting movements. It further indicates that the ability to integrate multisensory input is innate, and emerges as the developing brain interacts with the environment.
The superior colliculus (SC) is a major site of multisensory integration in the mammalian brain. The SC, as shown in FIG. 1, is located in the mammalian midbrain, and is homologous to the optic tectum of non-mammals. On grounds of differing connectivity and function, it can be divided into superficial and deep layers. The deep SC integrates multisensory input and participates in the generation of saccadic (rapid) eye movements. The superficial SC receives only visual input and does not participate in saccade generation.
The deep SC in mammals receives convergent inputs from the visual, auditory, and somatosensory systems. Sensory input arrives from many sub-cortical and extra-primary cortical regions of the brain. The deep SC sends its outputs to premotor circuits in the brainstem and spinal cord that control movements of the eyes and other structures. Neurons in the SC are organized topographically according to their receptive fields. Maps for the various sensory modalities are in register. The motor output of the SC is also topographically organized. Activation of neurons in a localized region of the SC leads, for example, to a saccade of a stereotyped direction and magnitude.
Multisensory enhancement (MSE) is a dramatic form of multisensory integration, in which the response of an SC neuron to an input of one sensory modality can be greatly increased by input of another sensory modality. MSE was first identified in the optic tectum of the rattlesnake, where visual and infrared stimuli can affect the activity of the same neurons. Percent multisensory enhancement is computed as:
%MSE=[(CMxe2x88x92SMmax)/SMmax]xc3x97100xe2x80x83xe2x80x83(1)
where CM is the combined-modality response and SMmax is the larger of the two unimodal responses. Percent MSE can range upwards of 1000%. Percent MSE is larger when the single-modality responses are smaller. This property is known as inverse effectiveness.
MSE is dependent upon the spatial and temporal relationships of the interacting stimuli. Stimuli that occur at the same time and place are likely to produce response enhancement, while stimuli that occur at different times and/or places are not likely to produce enhancement. MSE is also observed at the behavioral level. For example, a cat is much more likely to orient toward the source of a weak stimulus if it is coincident with another stimulus, even a weak one, of a different modality. MSE clearly helps animals detect targets. It is suggested that the function of MSE is to enhance the target-related activity of deep SC neurons.
Multiple observations from a variety of sensors increase the amount of information available for automated tasks such as detection and localization of events in the environment. Fusing inputs from multiple sensors involves transforming different sensor readings into a common representational format, and then combining them in such a way that the uncertainty associated with the individual sensor observations is reduced.
There are several components to the technological problem of muiltisensor fusion that have parallels with the neurobiology of the SC as described above. For example, sensor registration and alignment are issues in a multiple sensor environment. So is the implementation of a suitable, common representational format. The SC appears to solve both of these problems through the use of common topographical representations in the form of sensory maps, which allow multisensory alignment and implementation of common representational format.
The present invention relates to a method of determining spatial target probability using a model of multisensory processing by the brain. The method includes acquiring at least two inputs from a location in a desired environment where a first target is detected, and applying the inputs to a plurality of model units in a map corresponding to a plurality of locations in the environment. A posterior probability of the first target at each of the model units is approximated, and a model unit with a highest posterior probability is found. A location in the environment corresponding to the model unit with a highest posterior probability is chosen as the location of the next target.